| 1. |
- Höök, Lars, et al.
(författare)
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Dualistic dosage compensation and rapid evolution of expression balance in response to W chromosome degeneration in Leptidea butterflies
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The evolution of dimorphic sex chromosomes from initially homologous autosomes is generally explained by sex-specific selection to maintain linkage between a sex determining locus and genes that are beneficial to the same sex. While initially beneficial, the strong linkage and reduced recombination causes differentiation and degeneration of many initially shared genes. Reduced copy numbers can have severe consequences for the balance of gene expression levels between sex-linked genes and the rest of the genome. Consequently, dosage compensation has evolved independently in different lineages to mitigate the detrimental effects of unbalanced expression of sex-linked genes in the heterogametic sex. However, the variation in sex chromosome regulation in different lineages, puts the need to restore expression to ancestral levels into question. In particular, a general difference has been observed between male- (XY) and female-heterogametic (ZW) systems. In contrast to the X chromosome upregulation in heterogametic males in the XY-systems, the Z chromosomes are rarely upregulated in the heterogametic females in organisms with ZW-systems. Instead, the Z chromosomes are often downregulated in the homogametic males to achieve inter-sexual balance. Although progress has been made to understand what causes this discrepancy, comparative approaches are limited by long divergence times and ancient sex chromosome systems. An attractive approach is therefore to study the evolution of gene regulation on recently derived neo-sex chromosomes, formed through fusions between ancestral sex chromosomes and autosomes. Here, we investigated dosage compensation of neo-sex chromosomes in three closely related butterflies in the cryptic wood white clade (Leptidea). Importantly, the species have acquired multiple sex chromosomes, and dosage compensation could therefore have evolved repeatedly in the clade. Our analyses reveal a mixture of gene expression patterns which suggests that distinct modes of dosage compensation have evolved on the different Z chromosomes. In addition, we detect evidence that dosage balancing mechanisms have been rapidly recruited to the youngest neo-Z chromosome, to counteract an ongoing degeneration of neo-W gametologs. The results add to a growing list of examples where diverse dosage compensation mechanisms can evolve within a single species, and suggests that various regulatory mechanisms are not restricted to specific sex chromosome systems.
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| 2. |
- Höök, Lars, et al.
(författare)
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High-density linkage maps and chromosome level genome assemblies unveil direction and frequency of extensive structural rearrangements in wood white butterflies (Leptidea spp.)
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Tidskriftsartikel (refereegranskat)abstract
- Karyotypes are generally conserved between closely related species and large chromosome rearrangements typically have negative fitness consequences in heterozygotes, potentially driving speciation. In the order Lepidoptera, most investigated species have the ancestral karyotype and gene synteny is often conserved across deep divergence, although examples of extensive genome reshuffling have recently been demonstrated. The genus Leptidea has an unusual level of chromosome variation and rearranged sex chromosomes, but the extent of restructuring across the rest of the genome is so far unknown. To explore the genomes of the wood white (Leptidea) species complex, we generated eight genome assemblies using a combination of 10X linked reads and HiC data, and improved them using linkage maps for two populations of the common wood white (L. sinapis) with distinct karyotypes. Synteny analysis revealed an extensive amount of rearrangements, both compared to the ancestral karyotype and between the Leptidea species, where only one of the three Z chromosomes was conserved across all comparisons. Most restructuring was explained by fissions and fusions, while translocations appear relatively rare. We further detected several examples of segregating rearrangement polymorphisms supporting a highly dynamic genome evolution in this clade. Fusion breakpoints were enriched for LINEs and LTR elements, which suggests that ectopic recombination might be an important driver in the formation of new chromosomes. Our results show that chromosome count alone may conceal the extent of genome restructuring and we propose that the amount of genome evolution in Lepidoptera might still be underestimated due to lack of taxonomic sampling.
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| 3. |
- Höök, Lars, et al.
(författare)
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High-density linkage maps and chromosome level genome assemblies unveil direction and frequency of extensive structural rearrangements in wood white butterflies (Leptidea spp.)
- 2023
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Ingår i: Chromosome Research. - : Springer Science and Business Media LLC. - 0967-3849 .- 1573-6849. ; 31:1
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Tidskriftsartikel (refereegranskat)abstract
- Karyotypes are generally conserved between closely related species and large chromosome rearrangements typically have negative fitness consequences in heterozygotes, potentially driving speciation. In the order Lepidoptera, most investigated species have the ancestral karyotype and gene synteny is often conserved across deep divergence, although examples of extensive genome reshuffling have recently been demonstrated. The genus Leptidea has an unusual level of chromosome variation and rearranged sex chromosomes, but the extent of restructuring across the rest of the genome is so far unknown. To explore the genomes of the wood white (Leptidea) species complex, we generated eight genome assemblies using a combination of 10X linked reads and HiC data, and improved them using linkage maps for two populations of the common wood white (L. sinapis) with distinct karyotypes. Synteny analysis revealed an extensive amount of rearrangements, both compared to the ancestral karyotype and between the Leptidea species, where only one of the three Z chromosomes was conserved across all comparisons. Most restructuring was explained by fissions and fusions, while translocations appear relatively rare. We further detected several examples of segregating rearrangement polymorphisms supporting a highly dynamic genome evolution in this clade. Fusion breakpoints were enriched for LINEs and LTR elements, which suggests that ectopic recombination might be an important driver in the formation of new chromosomes. Our results show that chromosome count alone may conceal the extent of genome restructuring and we propose that the amount of genome evolution in Lepidoptera might still be underestimated due to lack of taxonomic sampling.
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| 4. |
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| 5. |
- Lundin, Karin, et al.
(författare)
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Cochlear implantation in the elderly
- 2013
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Ingår i: Cochlear Implants International. - 1467-0100 .- 1754-7628. ; 14:2, s. 92-97
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: To analyse complications and outcome of cochlear implant (CI) treatment in seniors receiving CIs during a 10-year period.METHODS:A total of 28 patients, 79 years or older (mean age 81.6 years), were evaluated and compared with a younger group of 76 patients, 20-60 years old (mean age 48.9 years). A retrospective study of the patients' records was performed. Data on per- and post-operative complications, pre- and post-operative speech perception, estimated cognitive skills, and social situation was extracted. A subjective score was assessed and correlated with post-operative performance.RESULTS: No severe per- or post-operative surgical complications were noted. Speech perception improved significantly after surgery (P < 0.001). The younger age group showed better results post-operatively for monosyllabic words (P < 0.01) compared with the older group with no difference seen for bi-syllabic words. In both the groups, there were no significant differences between patients living with or without social support.DISCUSSION:CI surgery for patients 79 years or older was well tolerated. Patients benefited greatly from the device with improved hearing. CI should not be denied older individuals who are otherwise in good health. Non-use in the elderly was associated with post-operative vertigo and tinnitus, severe disease and limited social support.
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| 6. |
- Näsvall, Karin, et al.
(författare)
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Activity profiles of regulatory elements and associations with the oogenesis-flight syndrome in a long-distance butterfly migrant.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The oogenesis-flight syndrome reflects the temporal allocation of energy resources between dispersal / migration and reproduction and is a key concept in research on migratory behaviour in animals. Here, we used an experimental set-up to assess how variation in host plant abundance affected the activity of regulatory elements in the painted lady butterfly (Vanessa cardui), a model species for insect migratory behaviour studies. The results indicate that recently eclosed females that had access to host plants invested in reproduction at an earlier stage and that variation in host plant abundance triggered significant differences in regulatory element activity via acetylation. By analysing functions of genes in the vicinity of significant differences in regulatory activity we pinpointed a set of categories that can be relevant for how females perceive the environment and allocate resources for either migration or reproduction. The functions of genes in the vicinity of differentially activated regions were associated with metabolism, egg shell formation, female receptivity, muscle activity, pheromone binding and mini-chromosome maintenance. Our results provide a first glimpse into the regulatory underpinnings of the oogenesis-flight syndrome and a starting point for more detailed understanding of the links between environmental variation, gene regulation and migratory behaviour in butterflies.
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| 7. |
- Näsvall, Karin, et al.
(författare)
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Base composition, codon usage and patterns of gene sequence evolution in butterflies.
- 2023
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Ingår i: Genome Biology and Evolution. - : Oxford University Press (OUP). - 1759-6653. ; 15:8
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Tidskriftsartikel (refereegranskat)abstract
- Coding sequence evolution is influenced by both natural selection and neutral evolutionary forces. In many species, the effects of mutation bias, codon usage and GC-biased gene conversion (gBGC) on gene sequence evolution have not been detailed. Quantification of how these forces shape substitution patterns is therefore necessary to understand the strength and direction of natural selection. Here, we used comparative genomics to investigate the association between base composition and codon usage bias on gene sequence evolution in butterflies and moths (Lepidoptera), including an in-depth analysis of underlying patterns and processes in one species, Leptidea sinapis. The data revealed significant G/C to A/T substitution bias at third codon position with some variation in the strength among different butterfly lineages. However, the substitution bias was lower than expected from previously estimated mutation rate ratios, partly due to the influence of gBGC. We found that A/T-ending codons were overrepresented in most species and there was a negative association between the magnitude of codon usage bias and GC-content in third codon positions. In contrast, the tRNA-gene population in L. sinapis showed higher GC-content at third codon positions compared to coding sequences in general and less overrepresentation of A/T-ending codons. There was an inverse relationship between synonymous substitutions and codon usage bias indicating selection on synonymous sites. We conclude that the evolutionary rate in Lepidoptera is affected by a complex interaction between underlying G/C -> A/T mutation bias and partly counteracting fixation biases, predominantly conferred by overall purifying selection, gBGC and selection on codon usage.
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| 8. |
- Näsvall, Karin, et al.
(författare)
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Host plant diet affects growth and induces altered gene expression and microbiome composition in the wood white (Leptidea sinapis) butterfly
- 2021
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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 30:2, s. 499-516
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Tidskriftsartikel (refereegranskat)abstract
- In a time with decreasing biodiversity, especially among insects, a detailed understanding about specific resource utilization strategies is crucial. The physiological and behavioural responses to host switches in phytophagous insects are poorly understood. Earlier studies indicate that a host plant switch might be associated with distinctive molecular and physiological responses in different lineages. Expanding the assessment of such associations across Lepidoptera will reveal if there are general patterns in adaptive responses, or if each switch event is more of a unique character. We investigated host plant preference, fitness consequences, effects on expression profiles and gut microbiome composition in two common wood white (Leptidea sinapis) populations with different host plant preferences from the extremes of the species distribution area (Sweden and Catalonia). Our results show that female Catalonian wood whites lack preference for either host plant (Lotus corniculatus or L. dorycnium), while Swedish females laid significantly more eggs on L. corniculatus. Individuals from both populations reared on L. dorycnium had longer developmental times and smaller body size as adults. This indicates that both environmental and genetic factors determine the choice to use a specific host plant. Gene expression analysis revealed a more pronounced response to host plant in the Catalonian compared to the Swedish population. In addition, host plant treatment resulted in a significant shift in microbiome community structure in the Catalonian population. Together, this suggests that population specific plasticity associated with local conditions underlies host plant utilisation in wood whites.
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| 9. |
- Näsvall, Karin, et al.
(författare)
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Nascent evolution of recombination rate as a consequence of chromosomal rearrangements.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Reshuffling of genetic variation occurs both by independent assortment of chromosomes and by homologous recombination. Such reshuffling can generate novel allele combinations and break linkage between advantageous and deleterious variants which increases both the potential and the efficacy of natural selection. Here we used high-density linkage maps to characterize global and regional recombination rate variation in two populations of the wood white butterfly (Leptidea sinapis) with distinct karyotypes. The recombination data were combined with estimates of genetic diversity and measures of selection to assess associations between chromosomal rearrangements, crossing over, maintenance of genetic diversity and adaptation. Our data show that the recombination rate is influenced by both chromosome size and karyotype, but that the difference in recombination rate between karyotypes is reduced as a consequence of a higher frequency of double crossovers in larger chromosomes. As expected from effects of selection on linked sites, we observed an overall positive association between recombination rate and genetic diversity in both populations. Our results also revealed a significant effect of chromosomal rearrangements on the rate of intergenic diversity change between populations, but limited effects on polymorphisms in coding sequence. We conclude that chromosomal rearrangements can have considerable effects on the recombination landscape and consequently influence both maintenance of genetic diversity and efficiency of selection in natural populations.
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| 10. |
- Näsvall, Karin, et al.
(författare)
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Nascent evolution of recombination rate differences as a consequence of chromosomal rearrangements
- 2023
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Ingår i: PLOS Genetics. - : Public Library of Science (PLoS). - 1553-7390 .- 1553-7404. ; 19:8
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Tidskriftsartikel (refereegranskat)abstract
- Reshuffling of genetic variation occurs both by independent assortment of chromosomes and by homologous recombination. Such reshuffling can generate novel allele combinations and break linkage between advantageous and deleterious variants which increases both the potential and the efficacy of natural selection. Here we used high-density linkage maps to characterize global and regional recombination rate variation in two populations of the wood white butterfly (Leptidea sinapis) that differ considerably in their karyotype as a consequence of at least 27 chromosome fissions and fusions. The recombination data were compared to estimates of genetic diversity and measures of selection to assess the relationship between chromosomal rearrangements, crossing over, maintenance of genetic diversity and adaptation. Our data show that the recombination rate is influenced by both chromosome size and number, but that the difference in the number of crossovers between karyotypes is reduced as a consequence of a higher frequency of double crossovers in larger chromosomes. As expected from effects of selection on linked sites, we observed an overall positive association between recombination rate and genetic diversity in both populations. Our results also revealed a significant effect of chromosomal rearrangements on the rate of intergenic diversity change between populations, but limited effects on polymorphisms in coding sequence. We conclude that chromosomal rearrangements can have considerable effects on the recombination landscape and consequently influence both maintenance of genetic diversity and efficiency of selection in natural populations.
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